Vacuum cleaners are generally known and are operated by electric current either from the mains supply or an incorporated power source, namely a storage battery or the like.
Vacuum cleaners draw a relatively high amount of electrical power from the respective power source and convert it into air power or suction power at a floor nozzle or a suction wand. The suction power is the product of the negative pressure and the volume flow rate or volume flow. When vacuuming with the floor nozzle attached, a preferred operating range with good efficiency; i.e., a good ratio of electrical power input to suction power output, is obtained at about half the maximum possible volume flow rate. Frequently, however, the floor nozzle or the end of the suction wand is taken off the floor and set aside, for example, when the user wants to move furniture, to cause the vacuum cleaner to follow him or her, or to go to another room to accept a phone call, or just to interrupt vacuuming for a short time. During such periods, the vacuum cleaner is usually not turned off by the user; rather, it continues to run at the maximum volume flow rate, but without suction power. From an energy point of view, it is particularly disadvantageous that in this condition, maximum power is drawn from the power source, but no suction power is available, and also not needed, at the floor nozzle. In addition to this, the noise typically emitted by a vacuum cleaner continues to be emitted during the entire phase of non-use.
Various proposals have been made to avoid unnecessarily high energy consumption by the suction fan, and further to prevent the noise associated with the operation of the suction fan from being emitted during periods of non-use, or to recognize a condition of non-use.
International Patent Publication WO 02/091899 A describes a method for recognizing a condition in which the vacuum cleaner is not used. The recognition is based on measured pressure values. To this end, provision is made to determine a minimum pressure value and a maximum pressure value from a plurality of successively measured pressure values, and to calculate the difference therebetween. If this difference is below a threshold (i.e., if only small variations in the measured pressure values are sensed during the period in which the pressure values are recorded), it is assumed that the user is currently not using the vacuum cleaner, so that the suction fan motor power is reduced.
The approach of U.S. Pat. No. 6,105,202 is also based on considering a variation of measured pressure values. This patent proposes that, by means of exactly one pressure sensor and predefined rules for processing measured pressure values, a vacuum cleaner that is activated but not in use be prevented from generating undesirably high noise levels and consuming unnecessarily high amounts of energy by reducing the speed of the suction fan when the measured pressure values do not or only slightly change; i.e., when a first time derivative of a series of measured pressure values remains under a threshold.
Japanese Patent Publication JP 2 243 125 A intends to recognize the condition of use by movements of the floor nozzle, and proposes to sense the movement of the floor nozzle using a sensor system that functions as a motion sensor to sense the rotation of a wheel of the floor nozzle. If, in this way, the floor nozzle is detected to be stationary for more than a predefined period of time, this should be usable to turn off the suction fan.
United States Patent Publication US 2010/0 281 646 A describes an operating method for a special type of vacuum cleaner, which is known as upright vacuum cleaner. This method intends to recognize the condition of use using a tilt sensor, so that a larger amount of electrical power is supplied to the suction fan when the appliance is tilted, because this is interpreted to indicate continued use, and that the power supply is reduced when the appliance is in an upright position.
German Patent Publication DE 10 2007 025 389 A describes an operating method for a vacuum cleaner, which aims at uniform noise generation. To this end, a controller controls the volume flow rate generated by the suction fan as a controlled variable. In this connection, however, it is not necessary to measure the volume flow rate generated at any one time and, therefore, the volume flow rate is not known. Instead, it is possible to use experimental data, according to which the volume flow rate depends on the particular floor covering. For example, for smooth floor surfaces it is higher than for carpeted floors. On this basis, it is sufficient to transmit information on the respective floor covering to the controller, so that a floor covering sensor may be used in place of a volume flow rate sensor, which is not needed here.
In German Patent Publication DE 689 16 607 T, a method for operating a vacuum cleaner is described in which the static pressure generated by the suction fan at any one time is measured by exactly one pressure sensor. When the measured static pressure increases, the suction fan power is increased. The increase of the suction fan power is canceled when the measured static pressure falls below a threshold. In order to prevent oscillations, German Patent Publication DE 689 16 607 T proposes that the threshold at which the increase of the suction fan power is canceled be below the threshold at which the increase of the suction power was previously initiated.